Electrical relay and contact assembly



Dec. '29, 1959 B. J. GREENBLOTT EI'AL 2,919,326

ELECTRICAL RELAY AND CONTACT ASSEMBLY 3 Sheets-Sheet 1 Filed May 1'7,1956 INVENTOR BERNARD J.GREENBL OTF MART|N J. KELLY AGENT Dec. 29, 1959B. J. GREENBLCTT ETAL 2,919,326

ELECTRICAL RELAY AND CONTACT'ASSEMBLY 3 SheetsSheet 2 Filed May 17, 1956B. J. GREENBLOTT ETAL 2,919,326

ELECTRICAL RELAY AND CONTACT ASSEMBLY 3 Sheets-Sheet .3

Filed May 17, 195

United States Patent ()fifice 9 26 ELECTRICAL RELAY CONTACT ASSENIBLYApplication May 17, 1956, Serial No. 585,508

15 Claims. (Cl. 200-104) This invention relates to an electrical relayand contact assembly, and particularly to an improved electrical contactassembly for use in relays or other electromechanical devices where highoperating speeds are required and contact bounce must be eliminated asmuch as possible.

The bounce or vibration of electrical contacts as they close isdeleterious to the life of the contacts and may adversely affect theoperation of the circuit which they govern. As higher operating speedsare attained, the problem of bounce elimination becomes more acute, inview of the increased velocity of the contacts.

It is accordingly an object of this invention to provide an improvedelectrical relay, and an electrical contact assembly therefor in whichthe contact bounce which occurs on the'closing of the contacts issubstantially or wholly eliminated.

Another object of the invention is to provide an improved electricalcontact assembly in which the frequency of vibration of the contactsprings is substantially lowered, although the total length of thesprings is sufficiently long to permit contact spring material ofsubstan tial cross sectional area to be employed.

A further object of this invention is to provide an improved electricalrelay and a contact assembly especially suited for automatic productionand assembly.

Still another object of this invention is to provide an electricalcontact assembly having an operating spring member which is constrainedby the inherent spring forces in the member from motion at at least twopoints falling substantially on nodes of'flexural vibration of thespring member. i

A further object of the invention is to provide an improved electricalcontact assembly having a reentrant or looped operating'spring member,in which one leg of the loop is constrained from motion by the inherentspring force in the member, and in which at least one other pointofrestraint is provided at a point at or near the bight of the loopedcontact member, so that the spring member is constrained atsubstantially two nodal points of the flexural vibration wave length ofthes pring member.

Yet another object of the present invention is to provide an improvedelectrical contact assembly in which a looped operating spring member isconfined in a suitable enclosure to provide a degree of frictionaldamping for reducing unwanted vibration'in the member.

The foregoing objects are attained in this invention by the provision ofa contact assembly in which a resilient spring member, or movablecontact member is arranged with a free end which is moved into or out ofengagement with a fixed contact member. The opposite endof the springmember is constrained from motion preferably by the inherent resilienceof the spring member, and additionally, a constraining force is appliedat an intermediate point along the length of the spring member, at ornear a point on the spring member which is a nodal point for flexuralvibrations in the spring member. Since the spring member is thuseffectively restrained at one of its ends and at or near a nodal pointalong its length, the flexural vibration is highly damped. Thus the freeend of the spring has little or no vibrating movement as a result of itsimpact with the cooperating stationary contact member when the contactsclose.

In order to employ a spring member having a cross sectional area ofsufiicient size to provide adequate mechanical strength, and yet toreduce the overall dimensions of the contact assembly, the springmembers are made in a re-entrant or looped configuration, approximatinga U-shape. In this manner the frequency of fiexural vibration is keptrelatively low without increasing the length of the contact assembly orreducing the crosssectional area of the spring members.

The operating spring members are enclosed in a slot in a block or baseof insulating material, so that their motion is'confined substantiallyto a single plane, and so that the friction between the springs and thewalls of the enclosing slot provides a degree of damping for anyvibration which may occur.

The improved relay of this invention comprises a contact assembly of thetype described above, and an electromagnetic operating structure foroperating the contacts. A common datum surfaceis provided from which allcritical dimensions of the relay are taken, so that indi-vidual partsmay be fabricated .and assembled without cumulative tolerances buildingup to a point where auto matic manufacturing operations would not befeasible. Onesurface of the relay yoke may be taken as the reference ordatum surface, for example, and all critical dimensions measuredtherefrom. A mating surface is provided on the base or contact block, towhich the magnet yoke is attached, and all fixed contact elements areaccurately located with respect to this surface. The movable contactelements are adaptedto be preformed or prestressed, so that they may beinserted in the contact assembly by machine operation and will have there quired amount of spring tension when so assembled. In this manner,the contact assembly and the electromagnetic operator portion of therelay may be made separately, with the assurance that the final asemblywill find all parts properly located so that little or no manualadjustment is required.

Other objects of the invention will be pointed out in the followingdescription and claims and illustrated in the accompanying drawings,which disclose, by way of examples, the principle of the invention andthe best mode, which has been contemplated, of applying that principle.

In the drawings:

Fig. l is a diagrammatic plan view of an electrical relay constructed inaccordance with a preferred embodiment of the invention.

Fig. 2 is a diagrammatic elevation view of the relay.

Fig. 3 is an isometric view of the relay, and

Fig. 4 is a schematic cross-sectional view of the contact assemblyillustrating certain of the relations between the various parts.

Similar reference characters refer to similar parts in each of theseveral views.

Referring now to the drawings, there is shown the details of anelectrical relay constructed in accordance with the invention andprovided with the improved contact assembly which forms a part of thesubject invention. The relay includes an electromagnetic operatingmechanism, and a plurality of electrical contacts adapted to be operatedby the operating mechanism, all in a unitary assembly.

Considering first the electromagnetic operating mechanism, a stationaryyoke structure 3 of magnetic material, having an E-shaped configuration,is provided, the outer Patented Dec. 29, 1959 I legs being attached byrivets 4 or other suitable fastening means to a base block 5, which ismolded or otherwise formed from suitable insulating material, such asthe socalled plastic materials. The center leg 7 of the stationary yokemember 3 has mounted thereon an energizing winding 8, which may be woundon any suitable type of bobbin and slipped onto the center leg 7 duringassembly of the relay.

A U-shaped armature 9 of magnetic material is provided, with the legs ofthe U notched at the ends as shown so that the armature is retained inplace by forked portions 10 of a suitable spring member 11, which isfastened to the yoke 3 by any suitable means, such as the rivets 12. Thespring member serves to position the armature on the yoke and to definethe pivot point for the legs of the armature.

A contact operating member 13, of suitable insulating material, isattached to armature 9 in any suitable way, as by molding thereto, oremploying other fastening means. Projections or shoulders of member 13engage legs 14 of the spring member 11, as most clearly seen in Figs. 1and 3, and the parts are proportioned and arranged so that a force isexerted on the contact operating member 13, and hence the armature 9,tending to pivot the bight of the U-shaped armature away from thestationary yoke. The projections or shoulders of operating member 13 arearranged to engage the surface of yoke 3 when the armature 9 isreleased, to thereby act as a stop which limits the travel of operatingmember 13.

When the operating winding 8 is energized, the flux created in the yoke3 attracts the armature 9 so that it swings at its pivot points againstthe yoke 3, to occupy the position shown in the drawings. The motionthus produced is utilized to operate the contacts as describedhereinafter.

It is to be pointed out that the contact assembly subsequently describedis not dependent upon the use of any particular contact operating meansand the electromag netic operator structure may take any number of formswell known in the art.

Considering now the details of the improved contact assembly, thedrawings illustrate a contact assembly which provides four contactpositions, each position being the equivalent of a transfer positionhaving a normally open contact, a normally closed contact, and a commoncontact. Each position includes at least a first and a second fixedcontact element such as those designated by reference characters 16 and18. Where the equivalent of a transfer position is provided, anadditional fixed contact element 16 is provided, so that two of theelements 16 lie on either side of a common fixed element 18. As shown,the fixed contact elements 16 and 18 may be stamped or otherwise formed,after which they are molded in place in the insulating base 5. The endsof the elements 16 and 18 which project from the left-hand side of therelay, as seen in the drawings, may be formed to act as pins or plugs,receivable by suitable sockets in a suitable mounting or holding blockfor the relay, not shown. Obviously, the number of contact positions maybe varied as desired.

Rectangular slots or openings 19 are provided in the base block 5, onefor each of the contact assemblies, to accommodate the movable contactsprings or members 20. The slots confine the motion of the movablecontact springs and additionally provide frictional damping 'as a resultof the movable springs rubbing on the sides of the slots, that is tosay, the Width of the slot is sufficient to permit the movable springsto flex during operation, with a small clearance, but in view of thelength of the springs and the fact that the springs are free to cantslightly within the slot, portions of the springs will rub on the wallsof the slot during the flexing so that some amount of frictional dampingis provided. a

Each of the movable spring members 20 is in the form of a looped orU-shaped length of suitable spring material. To increase the reliabilityof the contacts, the spring members are provided in pairs, with one pairbeing used for each normally open or normally closed contact. The springmembers 20 are preformed before assembly to provide the proper degree ofspring force when engaging the fixed contact elements, and are theninserted in the slots 19. One end of each contact spring member isprovided with a hook-shaped bend 22, which engages a slot 24 in thefixed contact element 16, thus anchoring the spring 20 in place, andadditionally providing an electrical connection to one end of spring 20.

As can be seen from the drawings, the other or free end 26 of spring 20is moved into or out of engagement with the fixed common contact element18, as a result of the operation of contact operating member 13, whichin turn is operated by armature 9 in response to energization of theelectromagnetic operating mechanism.

The contact assembly thus provided is of the type known as permissivemake, in which each of the movable contact springs is prestressed sothat when unimpeded, it will engage its free end with the commonstationary contact member with the required amount of contact pressureto insure a low contact resistance. The contacts are operated out ofengagement by forcing the movable contact away from the stationarycontact as a result of operation of the contact operating member, eitherby the electromagnet when the relay is energized 1n the case of anormally closed contact, or by the armature return spring when theelectromagnet is de-energized in the case of a normally open contact.Such an arangement is advantageous over the more usual flexure type ofcontact, since the work required for contact actuation is one-half thatrequired by flexure contacts. Moreover, by arranging the parts so thatthe contact actuating member moves clear andremains clear of the movablecontact spring when it engages the fixed contact element, the effects ofarmature rebound are eliminated insofar as contact pressure and contactbounce are concerned.

The spring rate of the movable contact member is dictated by a number ofrequirements, particularly reasonable manufacturing tolerances, for agiven type of spring material. The cross-sectional area and theeffective length determine the spring rate, for a given type ofmaterial, but since the cross-sectional area cannot be reduced belowthat required for maximum allowable safe stress limits, it follows that,for a given cross-sectional area, a predetermined length of spring isrequired, if the spring rate is to be within suitable limits. The use ofa U-shaped or reentrant spring member thus permits a total spring lengthtwice that which is available with a straight spring, in the sameavailable space.

A further advantage is gained in the use of the looped or re-entrantmovable contact spring, in that vibrational damping is obtained whichfurther obviates contact bounce. As may be seen from Fig. 4, the movablecontact member 20 has its one end 22 fixed from motion in the plane ofoperation, since the spring force retains the hooked end 22 of thespring in the slot 24 of the fixed contact element 16 under all statesand operating conditions. It can be shown that, for a curved bar havinga given total length, the frequencies of vibration are not only lowerthan those for a straight bar of the same length, but also that thenodes of the vibrations are forced toward the middle of the bar. Theconfiguration of the parts is such that spring forces of the movablecontact member at the hooked end 22 and at the free end are exerted atthe points designated by the referenced arrows 28 and 30, respectively.The unbalanced force thus created forces the looped portion of themovable contact member into engagement with the contact slot wall at thepoint designated by referenced arrow 32. It is further apparent that theoperating force, which is applied at the point designated by thereferenced arrow 34, enters the system at a point between the forcesexerted by the spring at points 30 and 28, so that, under all static*andoperating conditions, the-spring member is forced against the wallof'the contact slot at point 32.-

The restraint of the movable spring member 20' at the one end 22, and atthe point 32 near the middle of its total length causes an internaldamping of the spring member which acts to minimize vibrations occurringupon impact of the free or operating end Z6of the spring with the commonfixed constant member 18.

Thus the provision of a prestressed looped spring member constrained atone end and at a point near the center provides a contact structurewhich not only requires a minimum amount of space, but also leads toelimination of contact bounce.

Having thus described the particular features of the electromagneticoperator and the contact assembly, a number of features of the entirerelay assembly will now be described.

From the standpoint of mass production, it is desirable to limit thenumber of manual assembly operations and adjustments to a minimum,particularly the manual adjustment of the individual movable contactsprings. In the present invention, the parts are proportioned andarranged so that nearly all fabrication and assembly operations may becarried out by suitably designed machines. The. fixed contact elements16 and 18 are molded into the base block 5, which may be made of amaterial having a high degree of dimensional stability, so that thevarious dimensions may be held within close tolerances without unduemachining of the various surfaces after molding. Such machining as isnecessary may be done in a onepass operation after the base is molded.

By selecting a suitable datum surface, and dimensioning all partstherefrom, cumulative tolerance errors are eliminated. For example, thedatum surface may be chosen to be the surface of the magnet yoke 3against which the armature 9 seats. All parts are dimensioned from thissurface, and since this surface is accurately located with respect tothe contact assembly, as a resultof the base 5 being attached to theyoke 3 with this surface as an interface, it follows that all dimensionsmay be readily maintained Within reasonable tolerances when the contactassembly is fastened to the yoke.

The movable contact springs may be cut and preformed from suitablelengths of material, and thereafter inserted in their slots, all bymachine operation.

The yoke and armature may be made from any suitable magnetic material,such as sintered magnetic material and the assembly thereto of thespring 11, which may be preformed, can be carried out by a machineoperation. The contact operating member 13 can be afiixed tothe armature9 by any suitable means, such as riveting or molding, also by machineoperation.

In the final assembly, the legs of yoke 3 are riveted or otherwisefastened to the block or base 5, with the contactoperating memberinserted between the opposed movable contact fingers. Thereafter, theleads for the operating coil 8 are soldered or otherwise connected tosuitable pins in the block 5 which act as coil terminals for the relay,as shown in Fig. 3.

It can be seenfrom the foregoing that this invention provides a noveltype of electrical relay structure, embodying a number of featureslending the relay to mass production with very little manual assembly oradjustment procedures. Additionally, a unique type of electrical contactassembly is provided, economical in space and manufacturing cost, andproviding bounce-free operation. As previously pointed out, the contactstructure may be employed in devices other than relays,.such as cam ormanually operated switches.

While there have been shown and described and pointed out thefundamental novel features of the invention as applied toa preferredembodiment, it will be understood that various omissions andsubstitutions and changes in the form and details of the deviceillustrated and in its operationmay be made by those skilledinthe art,with-..

6 out departing from the spirit of the invention. It is the intention,therefore, to be limited only as indicated by the scope "of thefollowing claims.

What is claimed is: i

1. In a switching device, the combination comprising a first and asecond fixed contact element, a looped resilient contact spring memberhaving a first and a second straight portion connected by a bightportion with all of said portions lying in a common plane including saidfirst and said second fixed contact elements, said spring member beingprestressed to cause said straight portions to engage said fixed contactelements, contact operating means effective at times to engage'one ofsaid straight portions of said spring member and disengage it from theassociated fixed contact element, the other straight portioncontinuously engaging its associated fixed contact element and meansconfining the motion of said spring member in said plane.

2. 'In a switching device, the combination comprising a block ofinsulating material, a first and a second fixed contact element locatedon opposite sides of an opening in said block, a looped resilientcontact spring member having a first and a second straight portionconnected by a bight portion with all of said portions lying in a commonplane, said contact spring member being disposed in said opening andprestressed to cause said straight portions to engage said fixed contactelements, and contact operating means effective at times to engage oneof said straight portions of said spring member and disengage it fromthe associated fixed contact element, the other straight portioncontinuously engaging its associated fixed contact element.

3. In a switching device, the combination comprising a first and asecond fixed contact element, a looped resilient contact spring memberhaving a first and a second straight portion connected by a bightportion, each of said portions lying in the same plane and disposedbetween said fixed contact elements, the end of said first straightportion of said spring member remote from said bight portion engagingsaid first fixed contact element, and the end of said second straightportion of said spring member remote from said bight portionengagingsaid second fixed contact element, means for confining the motion ofsaid spring member in said plane, and contact operating means for attimes engaging one of said straight portions and moving said straightportion out of engagement with the associated fixed contact element, theother of said straight portions continuously engaging its associatedfixed contact element.

' 4. In a switching device, the combination comprising a first and asecond fixed contact element, a looped resilient contact spring memberhaving a first and a second straight portion connected by a bightportion, each of said portions lying in the same plane and disposedbetween said fixed contact elements, the end of said first straightportion of said spring member remote from said bight portion engagingsaid first fixed contact element, and the end of said second straightportion remote from said bight port-ion engaging said second fixedcontact element, means for confining the motion of said spring member insaid plane, means for restraining the motion of said spring member atsaid bight portion, and contact operating means for at times engagingone of said straight portions and moving said straight portion out ofengagement with the associated fixed contact element, the other straightportion continuously engaging its associated fixed contact element.

5. In a switching device, the combination comprising a first and asecond fixed contact element, a looped resilient contact spring having afirst and a second straight portion connected by a bight portion, eachof said portions lying in the same plane and disposed between said fixedcontact elements, said first straight portion being anchored to saidfirst fixed contact element, said second straight portion engaging saidsecond fixed contact element, operating meansfor moving said secondstraight portion out of ens gagement with said second fixed contactelement against the resilience of said member, and confining means forconfining the motion of said contact spring to said plane, saidconfining means frictionally engaging at least a portion of said contactspring.

6. An electrical contact assembly comprising, in combination, a baseblock of insulating material having a rectangular slot therein, a firstand a second fixed contact element disposed at opposite ends of saidslot, a looped resilient spring member disposed in said slot, saidspring member having first and second straight portions connected by abight portion and prestressed to cause the extremities of said first andsecond straight portions remote from said bight portion to engage saidfirst and second fixed contact elements, and a contact operating membereffective at times to disengage one of said straight portions of saidspring member from the associated fixed contact element, the other ofsaid straight portions remaining continuously engaged with itsassociated fixed contact element.

7. An electrical contact assembly comprising, in combination, a baseblock of insulating material having a rectngular slot therein, a firstand a second fixed contact element disposed at opposite ends of theslot, a looped resilient spring member disposed in said slot, saidspring member having first and second straight portions conneted by abight portion and prestressed to cause the extremities of said first andsecond straight portions remote from said bight portion to engage saidfirst and second fixed contact elements and to cause a portion of saidfirst straight section adjacent said bight portion to engage theadjacent end wall of said slot, and a contact operating member effectiveat times to disengage said second straight portion of said spring memberfrom its associated fixed contact element, the extremity of said firststraight portion remaining continuously engaged with said first fixedcontact element.

8. An electrical contact assembly comprising, in combination, a baseblock of insulating material having a rectangular slot therein, a firstand a second fixed contact element disposed at the opening of said slotand at opposite ends thereof, a looped resilient contact spring memberdisposed in said slot, said spring member having a first and a secondstraight portion connected by a bight portion, and prestressed so thatsaid first and second Straight portions engage said first and secondfixed contact elements, the lines of action of the spring forces on saidfirst and second fixed contact elements being staggered so that a forceis exerted on said bight portion to cause it to engage the end of saidslot associated with said first straight portion and said first fixedcontact element, and contact operating means for at times exerting aforce on the free end of said second. straight portion to therebydisengage it from said second fixed conact element, the line of actionof the force exerted by said contact operating means on the free end ofsaid second straight portion falling between the lines of action of saidspring forces, whereby a continuous force is exerted on said bightportion to engage it with the end of said slot adjacent said first fixedcontact element.

9. An electrical contact assembly comprising, in combination, a baseblock of insulating material having a rectangular slot therein, a firstand a second fixed contact element disposed at opposite ends of saidslot, said first fixed contact element having an opening formed thereinadjacent said slot, said second fixed contact element having a contactsurface adjacent said slot, a pair of prestressed looped resilientspring contact members disposed in said slot, each of said springcontact members having a first and a second straight portion connectedby a bight portion, said first straight portion having its free endshaped to engage the opening in said first fixed contact element, andsaid second straight portion having its free end adapted to engage thecontact surface of said second fixed contact element, the spring forceexerted by said spring member having a first line of action through saidfirst fixed contact element and a second line of action through saidsecond fixed contact element, said first and second lines of actionbeing staggered so that the resultant force causes the bight portion ofsaid spring members to engage the end wall of said slot adjacent saidfirst fixed contact element, and contact operating means effective attimes to exert a contact operating force on said second straight portionof said spring members to disengage them from said contact surface, theline of action of said contact operating force falling between saidfirst and second lines of action of said spring force, whereby acontinuous force is exerted on each of said bight portions to engagethem with the end Wall of said slot adjacent said first fixed contactelement.

10. A relay comprising a yoke of magnetic material having a first and asecond outer leg and a center leg, one surface of each of said legslying in a common datum plane, an armature pivoted on said first andsecond outer legs of said yoke for an angular motion in a directionsubstantially transverse to said common plane, biasing spring. means forbiasing said armature away from said yoke, an operating winding mountedon said center leg of the yoke and effective when energized to createflux in the yoke and thereby attract the armature to the yoke, a contactoperating member operatively connected to said armature, a base blockprovided with a contact assembly including a plurality of fixed contactelements molded therein and including a plurality of slots betweenopposite ones of said fixed contact elements, a plurality of movablecontact spring members, one for each set of opposed fixed contactelements, disposed in said slots, and each of said movable contactspring members having one end thereof disposed for operation by saidcontact operating member into and out of engagement with one of saidfixed contact elements and the other end engaged with the opposite oneof said fixed contact elements, a datum surface on said base block forreferencing all dimensions of said contact assembly, and means forfastening Said base block to said yoke with said common datum plane ofsaid yoke and said datum surface coplanar.

11. A relay comprising a yoke of magnetic material having a first and asecond outer leg and a center leg, one surface of each of said legslying in a common datum plane, an armature pivoted on said first andsecond outer legs of said yoke for an angular motion in a directionsubstantially transverse to said common plane, biasing spring means forbiasing said armature away from said yoke, an operating winding mountedon said center leg of said yoke and effective when energized to createflux in the yoke and thereby attract the armature to the yoke, a contactoperating member operatively connected to said armature, a base block ofinsulating material provided with a contact assembly including aplurality of slots extending therethrough, a plurality of fixed contactelements molded in said base block on opposite sides of said slots, aplurality of looped resilient contact spring members, one pair of saidspring members disposed in each of said slots, each of said membershaving first and second straight portions connected by a bight portion,the free end of first straight portion of each spring member beinganchored to an associated fixed contact element and the free end of saidsecond straight portion of each spring member engaging an associatedfixed contact element, the free end of said second straight portion ofeach spring member being adapted for engagement by said contactoperating member, a common datum surface on said base block forreferencing all dimensions of said contact assembly, and means forfastening said base block to said yoke with said common datum plane ofsaid yoke and said datum surface of the base block coplanar.

12. An electrical relay structure adapted for automatic productioncomprising a contact assembly and an electromagnetic operator assembly;said contact assembly including a. base block of insulating materialhaving a reference surface thereon, and a plurality of slots therein, aplurality of pairs of fixed contact elements molded in said block, onepair of fixed contact elements being provided for each of said slots anddisposed with one of the pairs of contact elements located at one end ofsaid slot and the other of the pair of contact elements located at theother end of said slot, a plurality of pairs of prestressed loopedresilient contact spring members, each having first and second straightportions connected by a bight portion, one pair of said spring membersbeing disposed in each of said slots so that said first and secondstraight portions engage the fixed contact elements associatedtherewith; said electromagnetic operator assembly comprising an E-shapedyoke of magnetic material having a reference surface including one sideof the outer legs of the yoke, an operating coil mounted on the centerleg of said yoke, an armature pivoted on the outer legs of said yoke, acontact operating member operatively connected to said armature, and abiasing spring operatively connected to said operating member, and meansfor fastening said contact assembly to said electromagnetic operatorassembly, with said reference surface of said contact assembly coplanarwith said reference surface of said yoke.

13. In a switching device, the combination comprising a pair of fixedcontact elements, a U-shaped resilient contact spring member having oneleg in continuous engagement with one of said fixed contacts and flexedto urge the other leg into engagement with the other of said fixedcontact elements, means normally holding said other leg away fromengagement from its related fixed contact element and operable at timesto permit said other leg to move into engagement with its related fixedcontact element, and antibounce means comprising means engaging saidspring member in the vicinity of a nodal point of fiexural vibrationalong the length of said spring member to dampen the vibration of thecontact spring member.

14. In a switching device, the combination comprising first and secondfixed contact elements, a U-shaped resilient contact spring memberhaving a first and a second leg connected by a bight portion, saidcontact spring member being prestressed and disposed with said first andsaid second legs engaging said first and said second fixed contactelements, means engaging said bight portion, and operating meansetfective at times for disengaging one of said legs of said springmember from the associated fixed contact element, the other of said legsremaining continuously engaged with its associated fixed contactelement.

15. A relay comprising a yoke of magnetic material having a first and asecond outer leg and a center leg, one surface of each of said legslying in a common datum plane, anarmature pivoted on said first andsecond outer legs of said yoke for an angular motion in a directionsubstantially transverse to said common plane, biasing spring means forbiasing said armature away from said yoke, an operating winding mountedon said center leg of the yoke and effective when energized to createflux in the yoke and thereby attract the armature to the yoke, a contactoperating member operatively connected to said armature, a base blockprovided with a contact assembly including a plurality of fixed contactelements molded therein and including a plurality of slots betweenopposite ones of said fixed contact elements, a plurality of movablecontact spring members, one for each set of opposed fixed contactelements, disposed in said slots, and each of said movable contactspring members having one end thereof disposed for operation by saidcontact operating member into and out of engagement with one of saidfixed contact elements and the other end engaged with the opposite oneof said fixed contact elements, a datum surface on said base block forreferencing all dimensions of said contact assembly, and means forfastening said base block to said yoke with said common datum plane ofsaid yoke and said datum surface coplanar, said contact assembly beingdisposed in said base block to be positioned between said first andsecond outer legs of said yoke.

References Cited in the file of this patent UNITED STATES PATENTS1,048,670 Fessenden Dec. 31, 1912 1,143,676 Williams June 22, 19151,702,490 Brach Feb. 19, 1929 1,839,034 Johnson Dec. 29, 1931 2,769,064Rowe Oct. 30, 1956 FOREIGN PATENTS 614,773 France Sept. 24, 1956

